Modfication in already FFS-III Assessed vessel

[Inspectengr]

Hello

We have a vessel on ammonical water service as per ASME SECTION VIII DIV 1.
It was imploded due to vacuum. And was restored due to mechanical jacks and pneumatic pressure.
It was derated after FFS level 3 assessment.the study included details of all the welded patches in analysis.

My question is that now we are planning to install platform structure on that platform. For that we need to install few welded patches on external surface.

Its a cladded vessel with CS oitside and SS inside.

In past we have observed cladding detachment in vessel owing to imploded incident.

What hazards are anticipated in welding or installation of structure on vessel.

External thickness and DYE PENETRANT TESTING of surface is satisfactory.


Does it unvalidate The ffs study fea analysis. Or should we check after welding from inside.
Also the quantum of modification is very less in comparison. 200 x 200 plates 10 plates.


Or am i thinking more.

Best regards
Hassan

 

[TGS4]

As I mentioned in the other post of this topic, any modifications to your vessel will immediately invalidate the original FFS.